Joining of ceramic materials to other ceramic materials or to a metal component has been a long standing problem. This problem is particularly troublesome where the joining technique is required to form a gas-tight or hermetic seal between the adjoining ceramic materials or the ceramic-metal components. Ceramic joining is typically accomplished when forming seals between the adjoining ceramic parts or forming seals between a ceramic and a metal part. The preferred ceramic joining techniques are brazing, glass fritting and diffusion bonding techniques. While such techniques are relatively common in many industrial applications, the seals are often unsuitable for use in severe operating conditions (e.g. high temperature and high pressure) typically associated with an oxygen transport membrane applications. In addition, as such techniques involve slowly heating the adjoining materials to temperatures ranging from about 400° C. to 1200° C. or higher, the large differences in thermal expansion between metals and ceramics make joining of a ceramic part to a metal part using these conventional techniques even more challenging. To that end, new glass-ceramic seal materials are currently being investigated for use in oxygen transport membrane applications and other severe operation applications.
Conventional techniques, such as diffusion bonding techniques, typically use radiant heating methods to effect the joining of parts and so the cycle times required to reach the target temperatures as well as the bonding time at the target temperature can be quite long, typically on the order of multiple hours, particularly where the bonding process is conducted at temperatures approaching 1600° C.
However, none of the aforementioned ceramic joining techniques are effective for producing high performance hermetic seals that are capable of functioning in severe environment applications. Accordingly, there is a need for improvements and modifications to these existing methods of joining ceramic parts and methods of joining ceramics to metals to make high performance hermetic seals and/or joints that are capable of functioning in high temperature and high pressure applications, such as applications involving oxygen transport membranes and solid oxide fuel cells where seals are often subjected to high temperatures in excess of 800° C. and pressures in excess of 100 psi.
An alternative joining process that is suitable for many ceramic materials is an infiltration joining process. In the infiltration joining processes, a mixture of polymer precursor, aluminum, boron and silicon is applied to the joint surfaces in the form of a paste, slurry, tape, film or ribbon and then heated in an inert atmosphere in a furnace. The joint forms through pyrolysis of the carbon-containing polymer precursor material, which subsequently reacts with the silicon in the presence of the aluminum and/or boron sintering aids to form an in-situ, high density silicon carbide. While the infiltration joining process shows promise in the field of ceramic joining, the durability and performance of such seals as well as the cycle time required to form the seal are not yet optimized.
The present invention provides an improved or enhanced method of sealing a first ceramic part to a second solid part made of ceramic, metal, cermet or a ceramic coated metal that overcomes the above-identified problems.